Results of family, twin and adoption studies indicate that genetics is of etiological importance in Bipolar Affective Disorder (BPAD). Investigations show that there is considerable family aggregation for bipolar illness. In these studies there is not only an excess of illness in the relatives of probands, but there is increased risk correlated with relatedness. Genetic research has resulted in promising leads for the location of disease-causing alleles. More recent molecular genetic techniques hold promise for discovery of the genetic mechanism(s) for bipolar illness. Recent discoveries of unstable DNA (aberrant expansion of exonic trinucleotide repeats) in the inherited neuropsychiatric disorders of Fragile X syndrome, myotonic dystrophy and Kennedy's disease have generated interest in whether expanding trinucleotide repeat sequences (TNRs) are related to psychiatric disorders, particularly schizophrenia and bipolar illness. This novel mechanism may have relevance because these psychiatric disorders exhibit two features which are common among the neuropsychiatric disorders with unstable DNA: nonmendelian inheritance patterns and genetic anticipation. This research tests the unstable DNA hypothesis of bipolar affective disorder (BPAD). The hypothesis to be tested is that there will be a significant shift toward larger products in probands than controls. A group of 50 probands with early onset bipolar affective disorder (DMS III-R) will be recruited for study. Early onset is defined as demonstrated symptoms of onset of a psychotic illness prior to age 20. All cases for this research study will be reviewed by a psychiatrist who is experienced in psychiatric diagnostic practice. After case review, the proband (and their family if under 18) will be approached for recruitment. Additional information (including sociodemographic, age of first symptoms, age of first treatment, age of first hospitalization, number of hospitalizations, and family history of psychiatric illness will be collected and validated. For DNA extraction 40ml of venous blood will be drawn from each person. DNA obtained from peripheral blood leukocytes of each proband and control will undergo molecular analysis. The GCRC facility will be used as needed for the blood draws.